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feat: 添加 java-9 新特性代码(https://www.wdbyte.com/2020/02/jdk/jdk9-feature/)
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‎core-java-modules/core-java-9/README.md‎

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## core-java-9
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当前模块包含 Java 9 新特性相关代码
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### 相关文章
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- [Java 9 新特性介绍](https://www.wdbyte.com/2020/02/jdk/jdk9-feature/)

‎core-java-modules/core-java-9/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>core-java-modules</artifactId>
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<groupId>com.wdbyte.core-java-modules</groupId>
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<version>1.0.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>core-java-9</artifactId>
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<version>1.0.0-SNAPSHOT</version>
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<name>core-java-9</name>
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<packaging>jar</packaging>
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<properties>
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<maven.compiler.source>9</maven.compiler.source>
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<maven.compiler.target>9</maven.compiler.target>
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</properties>
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</project>

‎core-java-modules/core-java-9/src/main/java/com/wdbyte/java9/Jdk9CollectionFactory.java‎

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package com.wdbyte.java9;
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import java.util.*;
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/**
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* java 9 - 集合工厂方法
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* 集合工厂方法创建的集合都是不可变只读集合，在改变时会抛出异常。
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* 对于 Set 和 Map 工厂方法常见的,创建时如果有 key 值重复，也会直接抛出异常。
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* 对于 Set 和 Map 工厂方法常见的,每个 JVM 运行周期里遍历的顺序是不定的。
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*
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* @author 达西 - 公众号：未读代码
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*/
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public class Jdk9CollectionFactory {
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public static void main(String[] args) {
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// 工厂方法创建集合
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List<String> stringList = List.of("a", "b", "c", "d");
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Set<String> stringSet = Set.of("a", "b", "c", "d");
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Map<String, Integer> stringIntegerMap = Map.of("key1", 1, "key2", 2, "key3", 3);
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Map<String, Integer> stringIntegerMap2 = Map.ofEntries(Map.entry("key1", 1), Map.entry("key2", 2));
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// 集合输出
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System.out.println(stringList);
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System.out.println(stringSet);
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System.out.println(stringIntegerMap);
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System.out.println(stringIntegerMap2);
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}
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public void hashCodeOf(){
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// 工厂可以自由创建新的实例或者复用现有实例，所以 使用 of 创建的集合，避免 == 或者 hashCode 判断操作
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List<String> stringList = List.of("a", "b", "c", "d");
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List<String> stringList2 = List.of("a", "b", "c", "d");
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System.out.println(stringList.hashCode());
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System.out.println(stringList2.hashCode());
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}
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/**
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* jdk 9 之前创建只读集合方式
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*/
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public void jdk9Before() {
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List<String> arrayList = new ArrayList<>();
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arrayList.add("达西");
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arrayList.add("未读代码");
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// 设置为只读集合
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arrayList = Collections.unmodifiableList(arrayList);
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// java.lang.UnsupportedOperationException
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// arrayList.add("test");
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// Set,Map 同理
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}
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}

‎core-java-modules/core-java-9/src/main/java/com/wdbyte/java9/Jdk9Http.java‎

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package com.wdbyte.java9;
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import java.io.IOException;
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import java.net.URI;
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//import jdk.incubator.http.HttpClient;
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//import jdk.incubator.http.HttpRequest;
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//import jdk.incubator.http.HttpResponse;
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/**
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* @author 达西 - 公众号：未读代码
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*/
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public class Jdk9Http {
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/**
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* 只有在使用 JDK9 时才可以放开注释语句，不然找不到类
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*
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* @param args
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* @throws IOException
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* @throws InterruptedException
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*/
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public static void main(String[] args) throws IOException, InterruptedException {
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//HttpClient client = HttpClient.newHttpClient();
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//URI uri = URI.create("http://www.tianqiapi.com/api/xxx");
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//HttpRequest req = HttpRequest.newBuilder(uri).header("User-Agent", "Java").GET().build();
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//HttpResponse<String> resp = client.send(req, HttpResponse.BodyHandler.asString());
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//String body = resp.body();
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//System.out.println(body);
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}
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}

‎core-java-modules/core-java-9/src/main/java/com/wdbyte/java9/Jdk9Interface.java‎

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package com.wdbyte.java9;
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/**
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* @author 达西 - 公众号：未读代码
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*/
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public class Jdk9Interface {
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public static void main(String[] args) {
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ChinaPeople chinaPeople = new ChinaPeople();
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chinaPeople.sleep();
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chinaPeople.eat();
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chinaPeople.doXxx();
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}
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}
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class ChinaPeople implements People {
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@Override
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public void sleep() {
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System.out.println("躺着睡");
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}
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}
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interface People {
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void sleep();
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default void eat() {
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drink();
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}
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default void doXxx() {
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drink();
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}
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private void drink() {
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System.out.println("喝水");
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}
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}

‎core-java-modules/core-java-9/src/main/java/com/wdbyte/java9/Jdk9Stream.java‎

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package com.wdbyte.java9;
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import java.util.List;
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import java.util.Optional;
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import java.util.stream.Collectors;
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import java.util.stream.IntStream;
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import java.util.stream.Stream;
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/**
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* * @author 达西 - 公众号：未读代码
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*/
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public class Jdk9Stream {
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/**
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* takeWhile ,从头开始筛选，遇到不满足的就结束了
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*
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* @param args
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*/
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public static void main(String[] args) {
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// takeWhile ,从头开始筛选，遇到不满足的就结束了
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List<Integer> list1 = List.of(1, 2, 3, 4, 5);
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List<Integer> listResult = list1.stream().takeWhile(x -> x < 3).collect(Collectors.toList());
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System.out.println(listResult);
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// takeWhile ,从头开始筛选，遇到不满足的就结束
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List<Integer> list2 = List.of(1, 2, 3, 4, 3, 0);
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List<Integer> listResult2 = list2.stream().takeWhile(x -> x < 3).collect(Collectors.toList());
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System.out.println(listResult2);
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}
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/**
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* dropWhile ,从头开始删除，遇到不满足的就结束了
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*/
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public void dropWhile() {
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// dropWhile ,从头开始删除，遇到不满足的就结束了
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List<Integer> list1 = List.of(1, 2, 3, 4, 5);
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List<Integer> listResult = list1.stream().dropWhile(x -> x < 3).collect(Collectors.toList());
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System.out.println(listResult);
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// dropWhile ,从头开始删除，遇到不满足的就结束
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List<Integer> list2 = List.of(1, 2, 3, 4, 3, 0);
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List<Integer> listResult2 = list2.stream().dropWhile(x -> x < 3).collect(Collectors.toList());
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System.out.println(listResult2);
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}
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/**
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* 使用 ofNullable 创建支持 null 的 stream
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*/
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public void ofNullable() {
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Stream<Integer> stream = Stream.of(1, 2, null);
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stream.forEach(System.out::print);
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System.out.println();
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// 空指针异常
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// stream = Stream.of(null);
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stream = Stream.ofNullable(null);
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stream.forEach(System.out::print);
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}
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/**
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* 重载迭代器
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*/
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public void iterate() {
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IntStream.iterate(0, x -> x < 10, x -> x + 1).forEach(System.out::print);
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}
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/**
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* Optional 转 Stream
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*/
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public void optionalToStream() {
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Stream<Integer> s = Optional.of(1).stream();
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s.forEach(System.out::print);
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}
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}

‎core-java-modules/core-java-9/src/main/java/module-info.java‎

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module net.codingme.feature.jdk9 {
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exports com.wdbyte.java9;
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//requires jdk.incubator.httpclient;
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// 只有在使用 JDK9 时才可以放开上面的注释语句，不然找不到模块
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}

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